1. Field of the Invention
This invention relates to the formation of nano-imprinting master. More specifically, the invention relates to methods for producing high resolution, high aspect ratio nano-imprinting masters.
2. Description of the Related Art
A desired configuration for nano-imprinting masters, which are used to transfer sub-micron patterns to another media by physical contact, comprises a pattern having features extending above a substrate surface. These features generally have high aspect ratios in that they are much taller than they are wide, with the smallest features less than 50 nm in width. Generally, high aspect ratios are useful when transferring patterns into polymeric films or curable fluids, since the pattern accuracy is enhanced with deeper impressions in the receiving polymer media. Sub-micron features must be firmly adherent to the substrate, since as masters, they will be used repeatedly to transfer the patterns. Pulling the master from the polymeric films may create stiction or fluid friction forces that will dislodge loosely adherent features in the master.
The following describe two methods for making nano-imprinting masters disclosed in the prior art. One method uses a subtractive method whereby the transfer pattern is generated by etching material from a blanket layer deposited on a substrate. FIGS. 1(a)-(e) (Prior Art) illustrates the subtractive process. One starts in FIG. 1(a) with a blanket layer 104 deposited on substrate 102. Generally SiNx is used for layer 104 and a silicon substrate for 102. A negative e-beam photo resist layer 106 is then applied to layer 104 as in FIG. 1(b). Exposure and development produces patterned layer 106′ as in FIG. 1(c). However, current negative e-beam resists are incapable of producing structures with a width D (ref 108) less than about 40 nm. Following etching of the SiNx layer 104, the remaining pattern dimensions D are too large to provide structures less than 40 nm, which are required for advanced pattern masters.
Another method of the prior art is an additive method, illustrated in FIG. 2(a)-(e) (Prior Art), 3 (Prior Art) and 4 (Prior Art). In this method an e-beam resist 202 is deposited directly on substrate 102, exposed and developed to form patterned layer 202′. This pattern is a negative image of the desired final pattern. The SiNx material 204 is then deposited over the e-beam resist patterned layer 202′ as shown in FIG. 2(c). However, the deposition of SiNx material into narrow trenches is difficult, and may produce defects and voids 302 at the bottom of the trench as shown in FIG. 3 (Prior Art). Following planarization (FIG. 2(d) Prior Art) and resist removal, the finished master is shown in FIG. 2(e). The outlined detail of FIG. 4 (Prior Art) shows that this process may result in poorly adherent structures 204′ due to voids and defects 302 at the interface with the substrate.
U.S. Pat. No. 6,753,130 discloses a method for patterning a carbon-containing substrate utilizing a patterned layer of a resist material as a mask and then safely removing the mask from the substrate without adversely affecting the substrate, comprising sequential steps of: (a) providing a substrate including a surface comprising carbon; (b) forming a thin metal layer on the substrate surface; (c) forming a layer of a resist material on the thin metal layer; (d) patterning the layer of resist material; (e) patterning the substrate utilizing the patterned layer of resist material as a pattern-defining mask; and (f) removing the mask utilizing the thin metal layer as a wet strippable layer or a plasma etch/ash stop layer. In this disclosure, the thin metal layer aids in transferring the pattern from the resist layer to the carbon substrate, and must be etched prior to oxidation of the carbon substrate. However, the suggested use of the preferred metal aluminum, may compromise pattern integrity because aluminum may oxide during the carbon substrate oxygen reactive ion etching step, altering the dimensions of the openings in the aluminum mask layer. For example, a 25 to 30 angstrom thick oxide, typical of the natural Al2O3 grown at room temperature, can produce a 5 to 6 nm error in the dimensions of the original Al mask openings. For dimensions less than 40 or 50 nm, this error is significant and unsuitable for the manufacture of high resolution masters. The same condition applies for other recommended metals such as copper and nickel, which are also oxidized in the carbon substrate oxygen based reactive ion etching step. The resist layer is of no help in defining the pattern transfer during the substrate oxidation, as it is also likely to be destroyed.
What is needed is a process for forming high resolution, high aspect ratio nano-imprinting masters that have good adhesion to the substrate and are capable of producing features below 40 nm.
U.S. Pat. No. 6,391,216 discloses a method for reactive-ion etching a magnetic material with a plasma of a mixed gas of carbon monoxide and a nitrogen-containing compound, the method comprising a step, in which a multilayered film comprising a magnetic material thin film having thereon a resist film formed on a substrate is exposed to an electron beam and then developed, to form a pattern on the resist film, a step, in which a mask material is vacuum deposited, a step, in which the resist is dissolved, to form a mask, and a step, in which a part of the magnetic material thin film that is not covered with the mask is removed by reactive ion etching with a plasma of a mixed gas of carbon monoxide and a nitrogen-containing compound, to form a pattern on the magnetic material thin film, and thus obtaining the magnetic material thin film finely worked.
U.S. Pat. No. 6,576,562 discloses a manufacturing method of semiconductor devices comprising forming a mask material having an aromatic ring and carbon content of 80 wt % or more on an object, forming a mask material pattern by etching the mask material to a desired pattern, and etching the object to transfer the mask material pattern as a mask to the object.
U.S. Pat. No. 6,673,684 discloses a method for producing an integrated circuit including providing a diamond layer above a layer of conductive material. A cap layer is provided above the diamond layer and patterned to form a cap feature. The diamond layer is patterned according to the cap feature to form a mask, and at least a portion of the layer of conductive material is removed according to the mask.
U.S. Patent Application 2004/0180551 discloses a carbon hard mask for patterning an aluminum layer in a microelectronics device. The carbon hard mask will release carbon during a reactive ion etch process, thereby eliminating the need to use CHF3 as a passivation gas. Portions of the carbon hard mask remaining after the RIE process are removed during the subsequent strip passivation process without the need for a separate mask removal step.
Japanese Patent JP11092971 discloses a process to enable simple etching with high resolution and accuracy by constituting a mask of Ti, Mg, Al, Ge, Pt, Pd; single metals and alloys or compounds essentially comprising one or more of these elements. Ti, Mg, Al, Ge, Pt, Pd, alloys or compounds essentially comprising these elements, hardly react with a CO—NH3 gas plasma, so they are suitable as a mask material. Especially Ti, its alloys, or compounds essentially comprising Ti are excellent. By using a mask comprising these materials, redeposition of contaminant on the objective material for etching does not occur, and sharp and accurate etching is possible. The objective material of etching is preferably a magnetic material permalloy or the like. When a resist film is used for pattern forming, various kinds of organic polymer films are used. The etching plasma gas is preferably a mixture gas of CO and a nitrogen-containing compound such as NH3 and amines.
Japanese Patent JP2003140356 discloses a method for forming a fine pattern including processes of depositing a mask material on a pattern formed on the surface of a second resist film, on the objective substrate, and then removing a first resist film and the second resist film to form the arrangement of a dot pattern made of the mask material on the objective substrate. This method is characterized in that the mask material used contains fine particles having aggregates of carbon atoms as the structural element.
Japanese Patent JP1202353 discloses a dielectric film selected from the group consisting of germanium nitride, titanium nitride, boron nitride, chromium nitride, zirconium nitride, cobalt nitride, phosphorus nitride silicon carbide, tungsten carbide, titanium carbide, chromium carbide, molybdenum carbide and zirconium carbide formed on a glass substrate to the thickness corresponding to the depth of the desired signal pits or guide grooves by a vacuum thin film forming technique. A resist pattern having the pattern of the desired signal pits or guide grooves is then formed thereon and the dielectric film exposed through the resist pattern is removed by etching and thereafter the resist pattern is removed.
Japanese Patent JP3252936 discloses a hard carbon nitride film formed as an etching layer on a substrate, on which a resist film is formed by coating. After exposing the photoresist film to irradiation of laser light, and developing, a resist pattern is formed to be used as a mask for etching of the hard carbon film. By removing the resist remaining on the surface, the surface protective film comprising boron nitride is thus obtained. As for the etching layer, thin film of aluminum, chromium, silicon, or oxides of these, or the substrate itself can be used instead of the hard carbon film. Thus durability of a stamper is improved.
Japanese Patent JP62167869 discloses a pattern formed by a photoresist on the substrate consisting of glass, and thereafter a Si film is formed thereon by vapor deposition. The substrate patterned with the Si film formed by removing the photoresist with a stripping liquid is subjected to the plasma polymerization with CH4 as an introducing gas to form about 0.5 micron i-carbon film. Cr is deposited thereon by evaporation to about 1000 Angstrom as the layer to adhere the metallic film to glass and thereafter. Ni is deposited by evaporation to about 1 micron on the metallic film to be patterned. Since the Cr has the good adhesiveness to glass, the Ni film is deposited on the substrate surface. The i-carbon surface has the weak adhesive power to both the Cr and Ni and therefore the film exfoliates gradually after the vapor deposition and the pattern is formed only on the surface exposed by the film.